Positioning device



March 14, 1961 P. A; GILOVICH 2,974,492

POSITIONING DEVICE Filed July 14. 1958 INVEN TOR. PAUL A. GILGV/Ch' AGENT United States Patent 2,974,492 POSITIONING DEVICE Paul A. Gilovich, Santa Clara County, Calif., assignor to International Business Machines Corporation, New York, N.Y. a corporation of New York Filed July 14, 1958, Ser- No. 748,213 11 Claims. (Cl. 6044.5)

This invention pertains to a hydraulic positioning device employing a fluid coupling between a driving and a driven piston and more particularly it pertains to means for maintaining the volume of fluid within the coupling constant at all times to preserve a precise relationship between the displacements of the two pistons.

Hydraulic positioning devices of the type employing a fluid connection between a driving and a driven piston have not been entirely satisfactory in applications where extreme accuracy is demanded for the reason that leaks in the coupling cause a decrease in the quantity of fluid' connecting the two pistons. Thus, when the driving piston is displaced a given amount, the driven piston is displaced somewhat less than its expected related amount due to the loss of fluid in the coupling. Therefore, the problem has been one of maintaining the fluid connection completely full at all times to preserve the relationship between the displacements of the two pistons.

In the past, this has been done by resetting both pistons to a known position, usually a home, zero, or starting position, and then by means of a pump and valve arrangement refilling the fluid coupling. Such an arrangement may obviously not be operated for extended periods of time with accuracy without being reset to zero and hence, it would be inapplicable for a non-returnto-zero positioning application. According to the present invention, however, a simple restrictive orifice has been employed, together with a detent for holding the piston after each displacement thereof, to provide the subject replenishment at such times. Thus, considerable simplification and economy have been efiected as well as providing a hydraulic positioning device for non-return-tozero applications using fluid coupled pistons.

Therefore, it is an object of this invention to provide an improved hydraulic positioning device.

It is another object of this invention to provide a "non-return-to-zero hydraulic positioning device employing a pair of pistons coupled by a continuously replenished fluid connection.

It is another object of this invention to provide a simplified means for maintaining a fluid coupling at constant volume between a driving and a driven piston.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings which disclose, by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

In the drawings:

Fig. l is a schematic illustration in section of the invention.

Fig. 2 is a perspective view proportionately reduced of one of the pistons of the piston adder" shown in Fig. 1.

Referring to Fig. 1 there is provided a housing I having an upper cylinder 3 and a lower cylinder 5 connected by a chamber 7. In the upper cylinder 3 is a movable piston 9 connected on one side to a shaft 11 which extends through the right end of cylinder 3. Shaft 11 has interstice 29.

2,974,492 Patented Mar. 14, 1961 ice a number of teeth 13 therein which engage a vertically operating pawl or detent 15, actuated by any suitable means (not shown) such as a solenoid. ,Detent 15 is arranged to engage teeth 13 when driven upwardly and to disengage when withdrawn downwardly. Its vertical alignment is maintained by disposing it in a slot 17 formed in a protrusion 18 on the outer casing of cylinder 3. A pointer 19 is shown formed on the end of shaft 11 to represent schematically any suitable member to be positioned by shaft 11.

In cylinder 5 is provided a piston adder 21 of a type such as shown in US. Letters Patent 2,197,867. Adder 21 is arranged to displace and combine a plurality of predetermined volumes of fluid to drive piston 9 to the right a related amount as measured from a pair of fixed stops 20 in cylinder 3 which establish the zero position thereof. Adder 21 comprises five generally cylindrical pistons 23 as best shown in Fig. 2. Pistons 23 are free to move within cylinder 5 as well as with respect to each other. Relative movement, however, between pistons 23 is limited by coupling them in tandem using interlocking lips or extensions 25 formed at each end thereof. This interlocking arrangement provides an interstice 29 between each pair of pistons 23. The first, or right hand, piston 23 however is firmly anchored by a screw 27 through housing 1. Each interstice 29 is connected to a conventional 3-way valve 31 by a groove 33 cut in one abutting face of the pistons forming the associated A flat chord 35 cut from each end of pistons 23 on the periphery thereof completes the fluid connection between valve 31 and interstice 29 for each piston 23; interstices 29 may be made in binary lengths,

Le. (as measured between extensions 25) interstice 29a is one unitlong, 29b is two units, 290 is four units and 29d is eight units. Any selected pair of pistons 23 may be spread apart by pressurizing the associated interstice therebetween, as in the case of valve 31d as shown in Fig. l, which is shown leading to an intake manifold 37 connected to a source P of hydraulic fluid under pressure. Valve 31 may also be conditioned to connect to a low pressure exhaust manifold 39 leading to a sump S, as shown by the condition of valves 31a-31c which, as shown, are so arranged. 'The low pressure in interstices 29a-29c keeps their associated pistons 23 compacted under the pressure within interstice 29d. Thus, as shown, the leftmost piston 23 has been moved to the left eight unit. In the foregoing manner, any combination of displacements may be achieved by the free end of adder 21 from zero to fifteen units by pressurizing selective interstices 29.

Finally, an orifice 41 has been provided connecting chamber 7 to intake manifold 37 in order to refill chamber 7 whenever an ullage has occurred therein, as explained below. In addition, orifice 41 will drain oflE any excess fluid should an overage occur in chamber 7. Manifold 37 is also connected to cylinder 3 via a conduit 43 to provide a return bias to piston 9.

In operation, selected valves 31 are conditioned to pressurize their associated interstices 29, as for example, valve 31d as shown in Fig. 1. The pressure in interstice 29d is thereby raised to that of source P and the leftmost piston 23 moves leftward eight units. All pistons to the right are driven together by this pressurizing of interstice 29d since their associated valves 31a-31c are conditioned to exhaust the fluid therebetween to sump S. The displacement of fluid in cylinder 5 transmits the pressure of source P to the left side of amount of displacement of piston 9 will be proportionate to that of adder 21 as determined by their respective radii. After each movement of piston 9, detent 15 is inserted into teeth 13. This engagement of detent 15 with teeth 13 provides a slight adjustment in the positioh of piston 9 whenever fluid has been gained or lost in chamber 7. If leakage has occurred in chamber 7 during its positioning, the pressure therein is relieved by the action of detent 15 so that the chamber 7 pressure drops to less than that at source P. This pressure differential between source P and chamber 7 causes some small flow through orifice 41 into chamber 7 until the differential is cancelled. Conversely, if an overage has occurred in chamber 7 the pressure differential will be reversed and the excess fluid will be drained off through the same orifice 41. However, it is to be appreciated that the usual problem is one of leakage. In the dynamic state when adder 21 is being positioned substantially no flow is present via orifice 41 and, to the fluid in chamber 7, orifice 41 looks like a substantially complete closure. In the above manner slight ullages and overages in chamber 7 are continuously eliminated after each movement of piston 9. Therefore, the only time that the fluid coupling is exposed to leakage is during the time piston 9 is in transit. As a result of this continuous adjustment of the fluid content in chamber 7, detent 15 should never engage the wrong tooth 13. However, if the loss of fluid in the coupling should become so great as to create this condition, proper compensation for such excessive loss may be had by merely enlarging orifice 41 to increase its flow.

To retract piston 9, detent 15 is disengaged and selected interstices 29 are opened to sump S. To effect complete retraction, all interstices are exhausted. This action lowers the pressure in all interstices 29 and hence in chamber 7. Therefore, a pressure differential will exist across piston 9 suflicient to provide a bias thereto notwithstanding the difference in effective facial areas thereof. The same pressure differential will exist across orifice 41. However, orifice 41 will again look like a closure to the fluid in its dynamic state. Therefore, the return bias on piston 9 collapses adder 21 allowing piston 9 to move leftward.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention; It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In an expansible chamber containing a noncompressible fluid, a pair of movable members defining variable limits of said chamber, means for moving one said member for transmitting said motion through said fluid to move the other said member proportionately, means for locking said members after each successive movement, and means including a fluid pressure source and an orifice into said chamber for maintaining the volume of said fluid constant in said chamber whereby leakage of said fluid past said members is compensated.

2. A positioning device comprising a chamber closed at each end by a movable member, said chamber being filled with a predetermined volume of liquid, means for displacing one of said members to move the other said member a proportionate amount, volume adjusting means for maintaining said volume of liquid constant to preserve said proportion, said adjusting means including means for holding both of said members, a source of filled with a predetermined volume of liquid, means for fluid under pressure, and an orifice for passing fluid bedisplacing one of said pistons to move the other said piston a proportionate amount, and volume adjusting means for maintaining said volume of liquid constant to preserve said proportion, said adjusting means including means for holding both of said pistons, a source of fluid under pressure, and an orifice for passing fluid between said pressure source and said chamber.

4. A positioning device comprising a chamber closed at each end by -a movable piston, said chamber being filled with a predetermined volume of liquid, means for displacing one of said pistons to move the other said piston a proportionate amount, volume adjusting means for maintaining said volume of liquid constant to preserve said proportion, said adjusting means comprising means for simultaneously holding both of said pistons, a source of fluid under pressure, and an orifice for passing said fluid between said pressure source and said chamber.

5. A positioning device comprising a chamber closed at a each end by a movable piston, said chamber being filled with a predetermined volume of liquid, a source of liquid under pressure for displacing one of said pistons to move the other said piston a proportionate amount, means for maintaining said volume of liquid constant to preserve said proportion, said means comprising means for holding both of said pistons after displacement thereof, and an orifice for passing liquid between said pressure source and said chamber during said holding.

6. A positioning device comprising a first and a second piston, a cylinder for housing each of said pistons, said pistons being displaceable with respect to said cylinder, a chamber interposed between said pistons, said chamber being filled with fluid for coupling said pistons, a source of fluid under pressure, means for displacing said first piston to move said second piston a proportionate amount via said fluid coupling, means for holding both of said pistons simultaneously, and an orifice arranged to pass fluid from said pressure source to said coupling to adjust the fluid within said chamber while holding said pistons, whereby said fluid volume is maintained constant to preserve said proportionate displacement relationship between said pistons.

7. A positioning device comprising a first and a second piston, a cylinder for housing each of said pistons, said pistons being displaceable with respect to said cylinder, a chamber interposed between said pistons, said chamber being filled with fluid for coupling said pistons, a source of fluid under pressure for displacing said first piston to move said second piston a proportionate amount via said fluid coupling, means for holding both of said pistons, and an orifice interposed between said pressure source and said coupling for adjusting the amount of said fluid in said chamber during the holding of said pistons, whereby said fluid volume is maintained constant to preserve said proportionate displacement relationship between said pistons. 8. A positioning device comprising a first and a second piston, a cylinder for housing each of said pistons, said pistons being displaceable with respect to said cylinder, a chamber interposed between said pistons, said chamber being filled with fluid for providing a driving connection between said pistons, a source of fluid under pressure for displacing said first piston to move said second piston a proportionate amount, means for holding both of said pistons after displacement thereof, and an orifice arranged to pass fluid from said pressure source to said coupling to replenish said chamber during the holding of said pistons, whereby said fluid volume is maintained constant to preserve said proportionate displacement relationship between said pistons.

9. A positioning device comprising a first and a second piston, a cylinder for housing each of said pistons, said pistons being displaceable with respect to said cylinder, a chamber interposed between said pistons, said chamber being filled with fluid for providing a driving connection between said pistons, a source of fluid under pressure for displacing said first piston to move said second piston a proportionate amount, means for holding both of said pistons in a predetermined relation to each other after displacement thereof, and an orifice interposed between said pressure source and said coupling for replenishing said chamber during the holding of said pistons, whereby said fluid volume is maintained constant to preserve said predetermined relation between said pistons.

10. In a hydraulic system having a driving piston, a driven piston, a hydraulic coupling between said pistons, and means for moving said driving piston, means for adjusting said coupling to maintain said coupling ata predetermined fluid volume comprising a source of fluid under pressure, an orifice arranged to pass fluid between said pressure source and said coupling to adjust the volume of fluid in said coupling, and means for aligning References Cited in the file of this patent UNITED STATES PATENTS 2,197,867 Klement April 23, 1940 2,305,302 Mazur Dec. 15, 1942 2,361,326 Silver Oct. 24, 1944 

